The present invention relates to a method of manufacturing a system for randomizing sector addresses, which is designed for use in, particularly, a hard disk drive and which efficiently detect errors in servo-sector addresses for identifying the servo sectors provided on a disk.
A hard disk drive (HDD) has a plurality of disks used as data storage media. A number of concentric tracks (also called xe2x80x9ccylindersxe2x80x9d) are provided on each disk. Each track consists of sectors of two types, i.e., servo sectors and data sectors. On the servo sectors, servo data is recorded. On the data sectors, user data is recorded. The servo sectors are arranged in the track, equidistantly spaced part from one another. Each servo sector has two recording areas for recording a cylinder address and servo burst data. (The cylinder address is used to identify the track, and the servo burst data represents burst patterns.) The data sectors are provided among the servo sectors. More precisely, one data sector or a few data sectors are arranged between two adjacent servo sectors. Some of the data are divided, each into two or more sub-data sectors, each of which is arranged between two adjacent servo sectors.
The HDD has a head, which is moved to a target position (or a target cylinder) over the disk in accordance with the cylinder address and the servo burst data. Each servo sector has another area, in which the servo-sector address (also known as xe2x80x9csector addressxe2x80x9d for short) is recorded. After the head has been positioned at the target track, the servo-sector address is used to designate a target sector at which data accessing will be performed. Thus, on each disk, the data sectors take specific positions with respect to the servo sectors. In the HDD, each data sector is identified by decoding the sector address recorded in the servo sector that corresponds to the data sector.
The servo data including the sector address is reproduced from a read signal read by the head. (The head is a read head which is either an MR head or a GMR head.) The servo data may not be reproduced correctly if the read signal is superimposed with noise or the like. If the servo-sector, in particular, is not correctly produced, data accessing may be performed at a wrong data sector. This is why the HDD recently developed has the function of checking the continuity of servo-sector addresses to determine whether the servo-sector address read is correct or not. More specifically, to access the data sector having the servo-sector address xe2x80x9c38,xe2x80x9d the HDD checks the servo-sector addresses xe2x80x9c36,xe2x80x9d xe2x80x9c37xe2x80x9d and xe2x80x9c38,xe2x80x9d one after another in the order mentioned. The use of any servo-sector address incorrectly reproduced due to the noise in the read signal supplied from the head is, therefore, prevented. The checking of the continuity of servo-sector addresses can effectively determine whether the servo-sector address read is correct or not, particularly when the noise influencing the serve-sector address is random noise.
One of the means used in the recent HDDs to accomplish high-density recording is a read/write head that has an MR (Magnetorisistive) head or a GMR (giant MR) head used as the read head. The read head can indeed excel in reproduction characteristic. However, as is known in the art, the magnetic sensitivity of its MR element abruptly changes, inevitably generating irregular noise called xe2x80x9cBarkhausen noise,xe2x80x9d and the read signal, i.e., the output signal, will be superimposed with this noise.
Unlike random noise, this noise is generated, depending on the waveform of the read signal. That is, the noise appears at specific positions of the signal waveform, though not always. Hence, the checking of the continuity of servo-sector addresses, described above, cannot always determine whether the servo-sector address read is correct, when the noise influencing the servo-sector address is Barkhausen noise, not random noise.
Assume that each servo-sector address is a data pattern composed of six bits 0 to 5, and that Barkhausen noise regularly appears at bit 5, or a specific position in the data pattern. If this happens, the servo-sector addresses xe2x80x9c3,xe2x80x9d xe2x80x9c4xe2x80x9d and xe2x80x9c5xe2x80x9d (or 000011, 000100 and 000101 in binary notation) will change to utterly different addresses xe2x80x9c35,xe2x80x9d xe2x80x9c36xe2x80x9d and xe2x80x9c37xe2x80x9d (100011, 100100 and 100101), respectively. In other words, if a reading error is regularly made (in bit 5 only, in this instance), the checking of the continuity of servo-sector addresses can no longer determine whether the servo-sector address read is correct or not. As a consequence, the data to be recorded in the data sector having the sector address xe2x80x9c38,xe2x80x9d for example, is inevitably recorded in the data sector having the sector address xe2x80x9c6.xe2x80x9d In summary, a specific bit of each sector-sector address will change, causing reproducing errors, if noise such as Barkhausen noise regularly appears at the specific bit of the servo-sector address. It is therefore impossible to determine whether the servo-sector address read is correct even if the continuity of servo-sector addresses is checked, and data accessing is performed at a wrong data sector.
The object of the present invention is to provide a disk drive in which it can be determined whether the servo-sector address read is correct, merely by checking the continuity of servo-sector addresses, even if an error may regularly occur at a specific one of the bits of each servo-sector address.
A disk driver according to the invention comprises: a disk on which a plurality of concentric cylinders are provided, each cylinder having servo sectors equidistantly arranged in circumferential direction of the cylinder, servo sectors including at least one data sector each and respectively having sector addresses recorded and randomized in accordance with specific translation rule; a head for reading the sector addresses from the servo sectors provided and reading and writing data from and in the data sectors; address generating means for translating the sector addresses read from the servo sectors by the head, back to the sector addresses specific to the servo sectors; and read/write means for designating a target servo sector by using the sector address of the target servo sector and causing the head to read and write data from and in the data sector provided in the target servo sector.
The sector addresses recorded on the same cylinder provided on the disk are translated to randomized ones, i.e., sector addresses that are not sequentially arranged in the initial order, in accordance with the prescribed rule. Thus, the servo-sector addresses have no continuity even if regular error occurs at a specific bit of each servo-sector address. The sector addresses arranged sequentially and reproduced from the disk differ from one another. Hence, the servo-sector addresses, back-translated by the address generating means, have no continuity. As a result, whether the reproduced sector addresses have an error or not can be reliably determined by checking the continuity of the back-translated sector addresses. In other words, the authenticity of the sector addresses can be determined. This prevents data from being recorded in a wrong data sector designated by an incorrect sector address.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.